1. Field of the Invention
This invention relates to an improvement in a fluid coking process. More particularly, this invention relates to a fluid coking process conducted in the presence of certain phosphorus-containing inorganic acid catalysts.
2. Description of the Prior Art
Fluid coking is a well known process which may be carried out with or without recycle of the heavier portion of the fluid coking zone effluent. As is well known in the art, the fluid coking process, as shown for example, in U.S. Pat. No. 2,881,130, which is hereby incorporated by reference, uses a fluid coking vessel and an external heating vessel. A fluid bed of solids, preferably coke particles produced by the process having a size in the range from about 40 to about 1000 microns is maintained in the coking zone by the upward passage of fluidizing gas, usually steam, injected at a superficial velocity usually between 0.3 and 5 feet per second. The temperature in the fluid coking bed is maintained in the range of about 850.degree. to about 1400.degree. F., preferably between 900.degree. and 1200.degree. F. by circulating solids (coke) to the heating vessel and back. The heavy oil to be converted is injected into the fluid bed and upon contact with the hot solids undergoes pyrolysis evolving lighter hydrocarbon products in vapor phase, including normally liquid hydrocarbons, and depositing a carbonaceous residue (coke) on the solids. The turbulence of the fluid bed normally results in substantially isothermal reaction conditions and thorough and rapid distribution of the heavy injected oil. The feed rate and temperature are controlled to maintain the bed in a fluidized state. Product vapors, after removal of entrained solids, are withdrawn overhead from the coking zone and sent to a scrubber and fractionator for cooling and separation. The end boiling point of distillate fractions obtained from the process is usually about 1050.degree. F. to about 1200.degree. F. and the remaining heavy ends are usually recycled to extinction.
U.S. Pat. No. 4,269,696 discloses an integrated fluid coking and gasification process in which a solid cracking catalyst is added to the coker chargestock.
U.S. Pat. No. 4,051,016 discloses a fluid coking process in which a relatively large amount of hydrogen sulfide is added to the coker fluidizing gas.
U.S. Pat. Nos. 4,169,041 and 4,229,283 disclose fluid hydrocoking processes in which oil soluble or oil dispersible metal compounds are added to the chargestock of the coker. The added metal compounds may be inorganic heteropoly acids such as phosphomolybdic acid and salts of organic acids. The hydrogen-containing fluidizing gas of the coking zone may also comprise hydrogen sulfide as disclosed in U.S. Pat. No. 4,229,283.
It has now been found that the presence of polymetaphosphoric acids, their salts and derivatives will provide advantages which will become apparent in the ensuing description.